There exist a number of biologically active compounds in nature, which are expected to be applicable to pharmaceutical products, such as lactacystin, myriocin, kaitocephalin, oxazolomycin and the like. All of these have an α-amino acid structure having an optically active quaternary carbon, and are considered to be deeply involved with physiological activity.
Therefore, construction of an asymmetric tetrasubstituted carbon center containing a nitrogen atom has been an important object of organic synthetic chemistry, and various synthesis methods have been reported.
The reported methods include a synthesis method of an optically active α-amino acid derivative based on the construction of an enantioselective carbon-carbon bond, which employs Strecker reaction or Mannich reaction (see references 1-7 below), and a synthesis method based on the construction of an enantioselective carbon-nitrogen bond, which employs proline, cinchonidine, 2,2′-isopropylidenebis(4-phenyl-2-oxazoline) (Ph-BOX) or β-isocupreidine as a catalyst (see references 8-14 below).    1. Journal of the American Chemical Society, (USA), 1998, Vol. 120, p. 5315    2. Angewandte Chemie International Edition, 2000, Vol. 39, p. 1279    3. Angewandte Chemie International Edition, 1998, Vol. 37, p. 3186    4. Journal of the American Chemical Society, (USA), 2000, Vol. 122, p. 762    5. Journal of the American Chemical Society, (USA), 1997, Vol. 119, p. 7153    6. Journal of the American Chemical Society, (USA), 2002, Vol. 124, p. 5640    7. Journal of the American Chemical Society, (USA), 2000, Vol. 122, p. 8180    8. Angewandte Chemie International Edition, 2002, Vol. 41, p. 1790-1793    9. Journal of the American Chemical Society, (USA), 2002, Vol. 124, p. 5656-5657    10. Journal of the American Chemical Society, (USA), 2002, Vol. 124, p. 6254-6255    11. Angewandte Chemie International Edition, 2003, Vol. 42, p. 975-978    12. Synlett, (USA), 2004, Vol. 12, p. 2115-2118    13. Angewandte Chemie International Edition, 2003, Vol. 42, p. 1367-1369    14. Journal of the American Chemical Society, (USA), 2004, Vol. 126, p. 8120-8121